A conventional inkjet printing system includes one or more printheads and an ink supply which supplies liquid ink to the printheads. The printheads eject ink drops through a plurality of nozzles and toward a print medium, such as a sheet of paper, so as to print onto the print medium. Typically, the nozzles are arranged along one or more axes such that properly sequenced ejection of ink from the nozzles causes characters or other images to be printed upon the print medium as the printheads and the print medium are moved relative to each other.
Many current inkjet printing systems, including those known as page wide array printing devices, utilize multiple printheads each of which contains multiple printhead dies. By ganging together multiple printhead dies, the number of nozzles and/or length of the printhead can be increased in an economical fashion, enabling faster, higher quality printing at low cost.
To effect color printing and accommodate a variety of media sizes, such devices often utilize print modes that require multiple passes and the overlapping of printhead elements of the printhead dies. Areas of printhead element overlap can be problematic in that each printhead element may have physical attributes or errors that cause one printhead element to release larger or smaller drops of ink relative to another printhead element, or cause errors in the relative position of dots created by the drops of ink. Such errors may be generally categorized as errors in image density uniformity and are to be avoided as they can cause inconsistent color and other reproduction errors. For example, the ink drop weight and drop size produced by different printheads often varies as a result of minute manufacturing differences in the size of the nozzles used in an inkjet printhead, different resistor characteristics in the heater element used to eject the ink droplets in the inkjet printhead, variations in the nozzle shape, and other differences from one printhead to another. Non-uniformity in printing may also be caused by factors such as aerodynamic variations, temperature fluctuations within the printhead, misalignment between adjacent printhead dies and misalignment between printheads. Any one of the above-listed non-uniformities, or a combination thereof, may adversely affect performance of the inkjet printing system.
Existing solutions for correcting errors in image density uniformity may require repeating time consuming measurements and calculations to create compensation regimens for each print mode. Other existing solutions may improve speed by utilizing corrective regimes based on generalized conditions (e.g. applying generalized corrective actions designed to address situations of perceived high, medium or low drop weight uniformity), but may sacrifice precision.